As the degree of integration of semiconductor devices such as VLSIs becomes high, a technique for forming a fine pattern with high precision becomes necessary. In such a pattern forming technique, the allowable dimensional precision is extremely severe. For example, in the most sophisticated field of such pattern forming technology, a dimensional precision of 3.sigma..ltoreq.0.1 .mu.m (where o indicates a standard deviation of average dimensions of masks or wafers) is required for the formation of patterns on 6-inch masks or 5-inch wafers. Further, in order to form patterns on masks or wafers in mass production, a dimensional scattering among a plurality of masks or wafers should be suppressed within 3.sigma..ltoreq.0.15 .mu.m. Apart from the above, in order to improve the productivity, a resist of high sensitivity is required, and, in addition, the sensitivity of a resist should be controlled to meet the sensitivity of the exposure apparatus (energy irradiating apparatus) to be used.
Resists have been formed heretofore in the following conventional manner:
First, a resist is coated on a substrate to be processed (e.g., a mask substrate) by the spin coating method or the dipping method. Next the resist film on the substrate to be processed (hereinafter referred to as substrate) is heated (baked) at a specific temperature by heating means such as an oven or a hot plate. The resist film is baked for a specific time, and thereafter the substrate with the baked resist film is left to cool naturally for about 20 to 30 minutes at room temperature and atmospheric pressure to cool it down to the room temperature. Thereafter, the resist film on the cooled substrate is exposed to light of a specific light quantity corresponding to the standard sensitivity of the resist. After specific development and rinse processes, resist patterns are formed.
With the above conventional method, however, it is difficult to adjust the sensitivity of each resist coated on a plurality of substrates, even if resists of the same type are used. Therefore, even under the same exposure and other process conditions for manufacturing semiconductor devices, proper exposure and other process conditions for each resist on a plurality of substrates are not necessarily ensured, it is not possible to form a satisfactory resist pattern on each substrate. In addition, the sensitivity of a resist film is not uniform even on a single substrate so that it is difficult to form a resist pattern having a uniform dimension even on a single substrate.